1. Field of the Invention
This invention relates to actuator or damping devices utilizing a piston. More specifically, the invention is a thermally driven piston assembly and position control system therefor with the piston being able to function as an actuator or a damping device.
2. Description of the Related Art
In the past, linear actuators required a transmission system to convert a motor's rotational energy into linear displacement. However, such linear actuators systems are not practical in many space-restricted applications. More recently, linear actuators use hydraulic or pneumatic driven pistons or have been made from stacks of piezoelectric materials that can generate a strong linear force when space is at a premium. However, hydraulically/pneumatically driven pistons require a pump to effect volumetric or pressure changes that move a piston. Piezoelectric-based linear actuators have low strain characteristics, thereby limiting their linear travel.
Currently, a variety of muscle-like polymer materials are being evaluated for use in actuator or damping devices owing to their ability to undergo large changes in strain and stiffness when activated. However, there is a need to provide simple and efficient actuator “packages” for these materials that capitalize on their large strain characteristics to achieve a linear actuator or damping response. Further, since several of these polymer materials have a tendency to exhibit creep, the actuator package that includes such polymer materials must be able to compensate for a material's creep characteristics.